Treatment of gas streams containing reduced sulfur compounds

Abstract

Gas streams containing non-condensible gases (NCG's) including reduced sulfur compounds, such as hydrogen sulfide, dimethyl sulfide, dimethyl disulfide and mercaptans, are treated to remove the NCG's from the gas stream. Following an optional initial gas-liquid contact to cool the gas stream to its adiabatic dewpoint and to remove particulates, the gas stream is subjected to an intimate gas-liquid contact with aqueous chlorine dioxide, in one or more contact stages, to oxidize the reduced sulfur compounds and other oxidizable compounds present in the gas stream, and then the gas stream is passed through an entrainment separator to remove entrained liquid droplets. Acidic gases produced in the oxidization stage and residual chlorine dioxide generally are removed from the gas steam by intimate gas-liquid contact of the gas stream with an aqueous neutralizing and reducing solution, in one or more contact stages, and ten the gas stream is passed through an entrainment separator to remove entrained liquid droplets.

What we claim is:  
     
       1. A method of removing oxidizable non-condensible gases (NCG's) comprising hydrogen sulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide, from a gas stream containing the same, which comprises: 
       contacting the gas stream with atomized water droplets having a droplet size distribution of about 5 to about 250 microns Sauter Mean Diameter (SMD) in one or more prescrubbing stages to cool the gas stream to its adiabatic temperature and to remove particulate matter out of the gas stream;  
       contacting the gas stream with an oxidizing liquid which is an aqueous solution of chlorine dioxide by intimate gas-liquid and gas-gas contact in one or more contact stages to oxidize reduced sulfur compounds and any other oxidizable compounds present in the gas stream, such contacting being effected by finely atomizing said aqueous solution of chlorine dioxide into the gas stream in each of said contact stages to form a spray of droplet size distribution of about 5 to about 250 microns Sauter Mean Diameter (SMD), and  
       passing the treated gases through an entrainment separator to remove entrained liquid droplets from the gas stream.  
     
     
       2. The method of  claim 1  wherein the droplet size distribution of the droplets in said one or more contact stages is about 10 to about 100 microns SMD. 
     
     
       3. The method of  claim 2  wherein the spray is formed by feeding said aqueous solution of chlorine dioxide to a dual-fluid spray nozzle under an atomizing pressure of about 20 to about 55 psig. 
     
     
       4. The process of  claim 3  wherein said aqueous chlorine dioxide solution has a concentration of about 2 to about 5 g/L. 
     
     
       5. The method of  claim 1  wherein the spray is formed by feeding said aqueous solution of chlorine dioxide to a dual-fluid spray nozzle under an atomizing pressure of about 25 to about 100 psig. 
     
     
       6. The process of  claim 5  wherein said aqueous solution of chlorine dioxide has a concentration of about 1 to about 10 g/L. 
     
     
       7. The process of  claim 1  wherein the quantity of chlorine dioxide contacting the gaseous stream is at least sufficient to oxidize the total oxygen demand content of the gas stream. 
     
     
       8. The process of  claim 7  wherein the molar ratio of chlorine dioxide used to the quantity of total oxygen den is about 1:1 to about 3:1. 
     
     
       9. The method of  claim 1  wherein said droplet distribution of the droplets in said one or more prescrubbing stages is about 10 to about 40 microns SMD. 
     
     
       10. The method of  claim 1  wherein the gas stream from the entrainment separator is contacted with an aqueous neutralizing and reducing solution by intimate gas-liquid contact in one or more contact stages to remove acidic compounds formed in the contacting step from the gas stream and to reduce any gaseous chlorine dioxide remaining from the contacting step and present in the gas stream, and the gas stream so treated is passed through a further entrainment separator to remove entrained liquid droplets from the gas stream, said contacting being effected by finely atomizing said aqueous neutralizing and reducing solution into the gas stream into each of said contact stages to form a spray of droplet size distribution of about 5 to about 100 micron SMD. 
     
     
       11. The method of  claim 10  wherein said droplet distribution of the droplets of the aqueous neutralizing and reducing solution is about 20 to about 60 microns SMD. 
     
     
       12. The method of  claim 11  wherein the spray is formed by feeding said aqueous neutralizing and reducing solution to a dual-fluid spray nozzle under an atomizing pressure of about 20 to about 55 psig. 
     
     
       13. The method of  claim 10  wherein the spray is formed by feeding said aqueous neutralizing and reducing solution to a dual-fluid spray nozzle under an atomizing pressure of about 15 to about 100 psig. 
     
     
       14. The method of  claim 10  wherein said neutralizing and reducing solution is provided by a Kraft pulp mill white liquor containing sodium hydroxide and sodium sulfide. 
     
     
       15. The method of  claim 10  wherein said neutralizing and reducing solution is provided by aqueous sodium sulfite or alkaline hydrogen peroxide. 
     
     
       16. The method of  claim 10  where the gas stream is passed through an additional entrainment separator to remove liquid droplets from the gas and to provide a discharge gas stream and the discharge gas stream is contacted with an aqueous medium by intimate gas-liquid contact in one or more contact stages to dissolve methanol vapor from the discharge gas stream, said contacting step being effected by finely atomizing said aqueous medium into the gas stream in each of said contact stages to form a spray therein. 
     
     
       17. The method of  claim 10  wherein the gas stream is passed through an additional entrainment separator to remove liquid droplets from the gas and to provide a discharge gas stream and said discharge gas stream is monitored for reduced sulfur compounds concentration and chlorine dioxide concentration, and the quantity of aqueous chlorine dioxide solution feed to the oxidizing step or the quantity of aqueous neutralizing and reducing solution feed to the neutralizing step are modified in response to changes in said monitored concentrations beyond predetermined values to return the respective monitored concentrations to below the predetermined values.